Robot wrist

ABSTRACT

A drive mechanism (62) for driving a mechanical joint (10) that includes first and second gimbal assemblies (14, 16) rotatably mounted within the interior of a support (18) and includes a decoupling mechanism (70, 72) in slidable engagement with the support (18) for effecting movement of the joint (10) in a compound yaw and pitch motion includes a yaw drive member (66) having a gear surface (82) in engagement with a drive shaft (84) having a beveled gear end portion (80) arranged to engage the gear surface (82). A pitch drive member (68) includes a gear surface (78) in engagement with a bevel gear end portion (76) of a second drive shaft (74). Both yaw and pitch drive members (66, 68) are pivotally connected to the decoupling mechanism (70, 72).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to mechanical joints and robot wrists, andin particular, it relates to robot wrists capable of compound pitch/yawmotion with continuous roll rotation.

2. Description of the Prior Art

A number of robot wrist designs and drive mechanisms have been developedin trying to achieve a wrist having dexterity equal to the human wrist.An ideal wrist should have 180° of singularity-free pitch/yaw motionwith continuous roll rotation. A brief summary of some of the prior artwrists is given below.

A rotary actuator mechanism is described in the Higuchi et al U.S. Pat.No. 4,009,644. The rotary actuator of the Higuchi et al Patent is notvery useful for the transmission of pitch, yaw and roll motion to a toolor implement member.

A number of robot joints are illustrated in the Vykukal U.S. Pat. No.3,405,406 and the Vykukal et al U.S. Pat. No. 4,046,262. The VykukalPatents describe hard-type space suits that permit the users inside thespace suits to move around somewhat unrestricted.

The Bolner U.S. Pat. No. 3,912,172 describes a back-drivable,direct-drive hydraulically-actuated pitch and roll actuator.

The Rosheim U.S. Pat. Nos. 4,194,437 and 4,296,681, which were issued tothe applicant of the present application, describe hydraulic servomechanisms which impart rotary movements to a device to be driven.

The Stackhouse U.S. Pat. No. 4,068,536 describes a remotely-driven,mechanical manipulator. The manipulator is controlled by threeconcentric drive shafts which terminate in a spherically-shaped wristmechanism.

The Totsuka U.S. Pat. No. 3,739,923 and the Niitu et al U.S. Pat. No.3,784,031 describe a manipulator arm having two parallel rotating driveshafts in a beveled gear system which translates the drive shaft'srotating motion to a bending pitch motion and rotary roll motion in atool member.

A mechanical wrist is described in German Patent 2,752,236 that includesthree electric motors providing pitch, yaw and roll, which are mountedon the outside of a housing with the inside of the housing being hollow.The wrist is used for holding welding tongs and the hollow insidehousing permits electrical power lines to be fed through the wrist.

The Molaug U.S. Pat. No. 4,107,948 describes a flexible robot arm thatis composed of a number of mutually connected rigid links beingconnected at one end to a drive means and at the other end to a toolmember.

Another robot arm is illustrated in the Wells U.S. Pat. No. 3,631,737.The robot arm of the Wells Patent includes a plurality of rigid tubularsections joined end-to-end by flexible joints to form an articulatedarm. The rigid sections are manipulated by slender control cables whichare attached to the respective sections and selectively extend andretract.

In addition, a number of well known universal joints are illustrated anddescribed on pages 16 and 17 of the Pictorial Handbook of TechnicalDevices by Pete Grafstein and O. Schwarz, published by the ChemicalPublishing Company, Inc. of New York, 1971. Although rotational motioncan be transmitted through the universal joints illustrated on pages 16and 17, the universal joints cannot be used in operations fortransmitting pitch, yaw and roll motion to an implement or a toolmember.

The development of robot arms and wrists is discussed in an articleentitled, "Robot Wrist Actuators," Robotics Age, November/December 1982,pages 15-22 written by the applicant of the present invention. In thisarticle, several characteristics are described which make robot wristsattractive. Disadvantages of prior art wrists are also discussed in thearticle.

SUMMARY OF THE INVENTION

The present invention includes an improved drive train for a robotwrist. The wrist includes a first and second gimbal assembly rotatablymounted within an interior of a support means. Each gimbal assembly hasmeans for transferring motion to the other gimbal assembly to effect yawand pitch motion. The wrist further includes decoupling means inslidable engagement with the support means for effecting movement of thewrist in a compound yaw/pitch motion. The improved drive train includesa yaw drive means having a gear surface and which is pivotally connectedto the decoupling means. A drive shaft with a beveled gear end portionis arranged to engage the gear surface of the yaw drive means to impartyaw motion to the wrist. The drive train further includes a pitch drivemeans having a pitch gear surface and which is pivotally connected tothe decoupling means. A drive shaft with a beveled gear end portion isarranged to engage the gear surface of the pitch drive means to impartpitch motion to the wrist. Means is also provided for rotational motion,said means for providing rotational motion being attached to the firstgimbal assembly.

In another aspect of the present invention, the wrist includes a conduituseful for passing optical fibers or wirings therethrough, extendingthrough each gimbal assembly. Each gimbal assembly includes an innergimbal member rotatably mounted to the support means and includes meansfor transmitting motion to another inner gimbal member of the othergimbal assembly. Each gimbal assembly also includes an outer gimbalmember rotatably mounted to the support means and having means fortransmitting motion to the other outer gimbal member of the secondgimbal assembly. The conduit means extends from the inner gimbal memberthrough a slot of the outer gimbal member. The slot has oppositelyfacing first and second surfaces, each surface having first and secondtracks. A first bearing means is disposed about the conduit and engagesa first track of a first surface of the slot. A second bearing is alsodisposed about the conduit and engages a second track of a secondsurface of the slot.

In another aspect of the present invention, the robot wrist includesfirst and second gimbal assemblies rotatably mounted within a supportmeans, with each gimbal assembly having means for transferring motion tothe other gimbal assembly. Drive means are operatively connected to thesupport means for effecting selective movement of the first and secondgimbal assemblies. Means are also included for transmitting rotationalmovement to the joint and includes a drive shaft extending from a baseand attached to the first gimbal assembly. Means for stabilizing thewrist engages the drive shaft, said means including an arm member thatis preloaded against the drive shaft and slidably engages the driveshaft and is pivotally attached to the support means.

In still a further aspect of the present invention, a linkage means isprovided for stabilizing a wrist having first and second gimbalassemblies. The linkage means has a first end that is pivotally attachedto a support means that supports the first and second gimbal assembliesand a second end that is pivotally attached to a base from which thedrive means that effects selective movement of the first and secondgimbal assemblies extends.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the wrist and drive train of the presentinvention.

FIG. 2 is a sectional view of with some portions shown whole forpurposes of clarity.

FIG. 3 is a perspective view of an alternative embodiment andalternative drive mechanism of the present invention.

FIGS. 4 and 5 are sectional views of the wrist of FIG. 3.

FIG. 6 is a perspective view of another embodiment showing the mechanismto stabilize the wrist using the central rotational drive shaft.

FIG. 7 is a sectional view perpendicular to the axis of the wrist ofFIG. 6.

FIG. 8 is a perspective view of another embodiment of a mechanism tostabilize the wrist using a scissors linkage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The wrist of the present invention is generally indicated at 10 inFIG. 1. The wrist 10 is similar in general concept to the wristdescribed in the Rosheim U.S. Pat. No. 4,686,866, issued to theapplicant of the present application. The present application isdirected to improvements in the wrist and the drive train.

The wrist 10 includes an upper gimbal assembly 12 and a lower gimbalassembly 14. The reference to upper and lower gimbal assemblies is forpurposes of convenience with respect to drawings and is not intended tolimit the present invention in any way.

The upper gimbal assembly 12 includes an outer upper gimbal 16 rotatablyattached to a housing 18 along a pivot axis 20, as best illustrated inFIG. 2. The lower gimbal assembly includes an outer lower gimbal 22pivotally attached to the housing 18 about a pivot axis 24. The gimbal16 includes a pair of spur gears 26. Similarly, the gimbal 22 includes apair of spur gears 28 that are in cooperative engagement with the spurgears 26 such that motion is transmitted between the gimbals 16 and 22through the spur gears 26 and 28. Movement of the outer gimbals causes"pitch" motion in the wrist 10. The gimbals 16 and 14 are pivotallyattached to the housing structure 18.

To accomplish movement of the wrist in a direction essentiallyperpendicular to the axis 20 and 24 ("yaw" motion), the wrist includesupper and lower drive shafts 30 and 32 attached to inner gimbals 31 and33, respectively. The upper inner gimbal 31 includes gears 34.Similarly, the lower inner gimbal 33 includes gears 36 that mate andcooperate with the gears 34 permitting pivoting of the wrist about axis38 and the upper drive shaft about axis 40, as best illustrated in FIG.2.

The outer gimbals 16 and 14 include slots 42 and 44 through which thedrive shafts 30 and 32, respectively, extend. To facilitate movementwithin the slots 42 and 44, the slots each include first tracks 46 and50, and second tracks 48 and 52. Although only one side surface of thegimbals is illustrated, it will be understood that a secondoppositely-facing surface with like tracks exists. The tracks 46 and 48are offset and the tracks 50 and 52 are offset. By offset is meant thatone track extends toward the center of the slot more than the other. Forexample, as illustrated in FIG. 1, track 46 extends inwardly more thantrack 48. The tracks 50 and 52 are also offset in a manner similar tothe tracks 46 and 48.

Bearings 54 and 56 are disposed about the shaft 30 to engage the tracks46 and 48, respectively. The bearings 46 and 48 permit movement of theupper drive shaft 30 within the slot 42 with minimal backlash.Similarly, bearings 58 and 60 are disposed about the shaft 32 and engagethe tracks 50 and 52, respectively, such that the drive shaft 32 travelsthrough the slot 44 with minimal backlash.

As can best be seen in FIG. 2, the cooperation between the lower driveshaft 32 and the upper drive shaft 30 through the respective gearportions 34 and 36 provides movement (pitch movement) of the drive shaft30 from a position that is coaxial to the drive shaft 32 to a positionthat is essentially perpendicular to the drive shaft 32 (or 90°). Itwill be understood that the drive shaft 30 is movable in exactly anopposite direction for 90° or a total of 180°. Movement in a directionperpendicular to the pitch movement (yaw movement) is caused by outergimbals 16 and 14 through their respective spur gear portions. Yawmovement extends for a total of 180°. If both the inner and outergimbals are actuated, a compound yaw/pitch motion results.

Motive force to the wrist 10 is provided by a drive mechanism generallyindicated at 62 in FIG. 1. The drive mechanism 62 transfers motive forcefrom a plurality of drive motors disposed within the housing 64 to thewrist 10. The driving mechanism 62 includes a yaw drive gimbal 66, apitch drive gimbal 68 and the previously mentioned lower drive shaft 32.The gimbal 66 is pivotally attached along the axis 24 to a firstdecoupling member 70 in circumferential slidable engagement with thehousing structure 18. In a similar fashion, the drive gimbal 68 ispivotally attached to a second decoupling member 72 about an axis 73which is also in circumferential slidable engagement with the housingstructure 18. It will be appreciated, that the decoupling member 70 and72 also rotate circumferentially around the housing structure 18 withrespect to each other such that decoupling of the wrist during compoundyaw/pitch motion occurs. Both decoupling members 70 and 72 are inslidable engagement with the housing structure 18 through bearings.

Motive force is imparted to the drive gimbal 68 through rotating shaft74 whose upper end portion includes gears 76 that engage a gear surface78 of the gimbal 68 in an arcuate arrangement so that pivoting can occurabout axis 73. The gear surface 78 extends along one side of the gimbal68. Similarly, the drive gimbal 66 includes a gear surface 80 disposedalong one side of the gimbal that is cooperatively engaged by gears 82which comprise the end portion of a rotating drive shaft 84. The gimbal66 is arcuately shaped with the gear surface arcuately arranged so thatpivotal movement of the drive gimbal about axis 24 occurs.

To minimize backlash and facilitate precision movement, both drivegimbals 62 and 68 are preloaded. For example, the drive gimbal 66 ispreloaded against idler rollers 86 and 88 which are mounted on thehousing 64 through mounting bracket 90, as best illustrated in FIG. 1.As best illustrated in FIG. 2, a bearing 88 is positioned between thelower drive shaft 32 and the gimbal 66 in a slot of the gimbal 66.

Similarly, the drive gimbal 68 is preloaded against an idler roller 89(illustrated in FIG. 1) that is mounted on the bracket 90 on a side ofthe gimbal 68 opposite from the gear surface 78. The gimbal 68 ispreloaded against the idler roller 89 and a bearing 91 is disposed in aslot of the gimbal 68 between the drive shaft 30 and the gimbal 68.

An electric motor 92 is disposed within the housing 64 and providesmotive force to the drive shaft 32 through a gear reduction assembly 94to provide rotational motion to the wrist 10. The drive shaft of themotor 92 is held in aligned rotation through engagement of bearings 96disposed on a side of the gear reduction assembly 96 opposite from themotor 92.

The shaft 84 is rotated by electric motor 98 which is directly connectedto the shaft 84 through coupling 100. Similarly, rotational movement tothe shaft 74 (which is illustrated in FIG. 1) is supplied by electricmotor 102 (which is depicted in FIG. 2 as extending outwardly from thefigure). The motor 102 is directly connected to the shaft 74 throughcoupling 104.

It will be appreciated that rotational movement of the shaft 84 istranslated into yaw motion through the gimbal 66. Rotational movement ofthe shaft 74 is translated into pitch motion through the gimbal 68.Rotation of both shafts 74 and 84 will provide a compound pitch-yawmovement of the wrist of the present invention through decoupling actionof the members 70 and 72 as described previously. Rotational movement isimparted to the wrist through rotation of the drive shaft 32 by motor92.

The lower drive shaft 32 includes an inner passage 106 and the upperdrive shaft 30 also includes an inner passage 108. The passages 106 and108 are open at their gear end portions 36 and 34 and permit placementof wires, fiber optic lines, fluid or pneumatic lines for use at thedistal end of the drive shaft 32.

An alternative embodiment of the present invention is generallyindicated at 120 in FIG. 3. The wrist 120 includes a housing 122 and afirst gimbal assembly 124 and a second gimbal assembly 126. The firstgimbal assembly includes an outer gimbal 128 that is pivotally attachedto the housing 122 about axis 130. Similarly, the gimbal assembly 126includes an outer gimbal 132 pivotally attached to the housing 123 aboutan axis 134 that extends substantially parallel to the axis 130. Thegimbals 128 and 126 include spur gear sections 136 and 138,respectively, that cooperatively engage each other to transmit movementbetween the gimbals 128 and 134, as best illustrated in FIG. 5. Thegimbal assembly 124 further includes an inner gimbal 140 having spurgear sections 132 disposed on opposite ends thereof, as best illustratedin FIG. 4. The inner gimbal 140 is pivotally attached to the housing 122about axis 144. Similarly, the gimbal assembly 126 includes an innergimbal 146 having spur gear portions 138 positioned on opposite ends ofthe gimbal 146, and pivotally attached to the housing 122 along axis150. The axis 150 is substantially parallel to the axis 144.

Each of the gimbals, 140, 128, 146 and 132 includes slots or openingsthrough which conduits 152 and 154 extend. As best illustrated in FIGS.4 and 5, the conduit 152 extends through the gimbals 128 and 140 and ispivotally attached to the gimbal 140. Similarly, the conduit 154 extendsthrough the gimbals 132 and 146 and is pivotally attached to the gimbal146, as best illustrated in FIG. 5. The conduits 152 and 154 are used tofacilitate electrical wiring, fiber optic cables, fluid or pneumaticlines, to a distal end of the conduit 152.

To facilitate movement of the conduit 152 with respect to the gimbal128, bearings 156 and 158 are provided around the conduit 152. As bestillustrated in FIG. 4, the bearing 156 is preloaded against one surfaceof the slot of the gimbal 128 while the bearing 158 is preloaded on anoppositely facing surface of the slot of the gimbal 128.

To provide motive force to the wrist 120, a coaxially disposed uniquedrive train 160 is provided. The drive train 160 includes rotationaldrive shaft 162, pitch drive shaft 164 and yaw drive shaft 166. Thedrive shafts 162, 164 and 166 are disposed coaxially with respect toeach other. The pitch drive shaft is disposed within the yaw drive shaft166 and extends outwardly therefrom through a distal end. Similarly, therotational drive shaft 162 is disposed within the pitch drive shaft andis preferably the same member as the conduit 154. The drive shaft 162(conduit 154) extends out of a distal end of the pitch drive shaft 164.Each of the drive shafts are suitably connected to an electric motor(not shown) in a manner that is well known.

To impart rotational movement to the wrist of the present invention, thedrive shaft 162 (conduit 154) is rotated about the axis 161 and theentire wrist is rotated.

To impart pitch movement, the pitch drive shaft 164 includes bevel gearportion 168. The gimbal 132 includes a cooperating bevel gear 170 thatcooperates with the gear portion 168. An idler roller 172 preloads thegear 170 against the gear portion 168. Rotational movement of the shaft164 is translated into pivotal movement of the gimbal 146 about the axis150.

The yaw drive shaft 166 also includes a bevel gear portion 174. A bevelgear yaw drive member 176 is pivotally attached to the housing 122 alongthe axis 150. The drive member 176 includes a bevel gear portion 178that cooperatively engages the bevel gear 174 of the shaft 166. An idlerroller 180 provides a force to preload the gear portion 178 incooperative engagement with the gear portion 174. It will be appreciatedthat rotational movement of the shaft 166 is transmitted into pivotalmovement of the housing along the axis 150.

An alternative embodiment of the wrist of FIGS. 3-5 is generallyindicated at 200 in FIGS. 6-7. In most respects, the embodiment 200 issimilar to the wrist illustrated in FIGS. 3-5 except for the drivetrain, and a mechanism for minimizing backlash during movement of thewrist.

The wrist 200 includes a housing 202, a first gimbal assembly 204 and asecond gimbal assembly 206. The housing 202 is rotatably secured withina collar 208 through bearings 210 that are circumferentially disposedbetween the collar 208 and the housing 202. The gimbal assembly 204includes an outer gimbal 212 having spur gear end portions 214 andpivotally attached to the housing 202 along an axis 216.

Similarly, the gimbal assembly 206 has an outer gimbal 218 having spurgear end portions 220 and pivotally attached to the housing 202 alongaxis 222. The axis 222 is substantially parallel to the axis 216.

The gimbal assembly 204 also has inner gimbal 224 with spur gear endportions 226 and is pivotally attached to the housing 202 along axis228. Similarly, the gimbal assembly 206 has inner gimbal 230 with spurgear portion 232 in cooperative engagement with the spur gear portion226 and is pivotally attached to the housing 202 along an axis 233.

A drive shaft 234 for providing rotational motive force to the wrist 200extends through the gimbal 218 and is attached to the gimbal 230 in amanner similar to the one described with reference to the embodiment ofFIGS. 3-5. A conduit 236 is attached to the gimbal 224 and extendstherethrough and through the gimbal 212 in a manner also similar to theembodiment of FIGS. 3-5. Electrical wires, fiber optic cables, fluid orpneumatic lines may be disposed within the passage of the drive shaft234 and the passage of the conduit 236 to a tool member (not shown)located at a distal end of the conduit 236.

Push-pull rod 238 extending from a housing 240 provides motive force foryaw rotation of the wrist 200 through link 242. The link 242 ispivotally attached at one end to the push-pull rod 238 and at anotherend to the collar 208.

A push-pull rod 244 extends through the housing 240 and travels alongthe general direction indicated by arrow 246 and is connected to thecollar 208 by link 248. The link 248 is pivotally attached to the rod244 at one end and pivotally attached to the collar at another end.

To stabilize the wrist and decrease possible backlash, the wrist isprovided with a guidance gimbal 250 having a pair of arms 261 and 262defining a slot 263. The gimbal 250 is pivotally attached to the collar208 by pivot pins 252 and 254. As best illustrated in FIG. 7, theguidance gimbal 250 is preloaded against the drive shaft 234 by idlerrollers 256 and 258. A bearing 260 is interposed between the drive shaft234 and the arm 262 of the gimbal 250. It will be appreciated, as thewrist 200 is actuated, that the arm 262 of the gimbal 262 will travelbetween the idler rollers 256 and 258 and the bearing 260.

An alternative method of stabilizing the wrist 300 is illustrated inFIG. 8. Since many of the elements of the wrist of FIG. 8 are the sameas the elements of the wrist of FIGS. 6 and 7, like reference characterswill be used to indicate like elements.

A scissors linkage 302 includes a lower link 304 pivotally attachedthrough a pin 306 to an upper link 308. The upper link 308 is pivotallyattached to the collar 208 by pivot pin 310 engaging a tab member 312that is fixedly attached to the collar 208. The bottom link 304 ispivotally attached to the housing 240 through pivot pin 314 pivotallyattaching the link 304 to tab 316, which is fixedly attached to thehousing.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A mechanical joint comprising:support means having an interior; first and second gimbal means rotatably mounted within the interior, each gimbal means having means for transferring motion to the other gimbal means so that yaw and pitch motion is effected; decoupling means in slidable engagement with the support means for effecting movement of the joint in a compound yaw and pitch motion; yaw drive means having a yaw gear surface and pivotally connected to the decoupling means; a yaw drive shaft with a yaw gear end portion arranged to engage the gear surface of the yaw drive means; pitch drive means having a pitch gear surface and pivotally connected to the decoupling means; a pitch drive shaft with a pitch gear end portion arranged to engage the gear surface of the pitch drive means; and means for providing rotational motion connected to the first gimbal means.
 2. The joint of claim 1 wherein the decoupling means includes a first and a second decoupling ring in rotational relationship with each other and the support means, the yaw drive means being pivotally attached to the first decoupling ring and the pitch drive means being pivotally attached to the second decoupling ring.
 3. The joint of claim 1 wherein the yaw drive shaft, the pitch drive shaft and the means for providing rotational motion are coaxially disposed with respect to one another.
 4. The joint of claim 1 and further including:means for stabilizing movement of the yaw drive means; and wherein the yaw drive means is disposed between the means for stabilizing movement and the yaw drive shaft.
 5. The joint of claim 4 wherein the means for stabilizing movement includes roller means engaging a surface of the yaw drive means.
 6. The joint of claim 1 and further including:means for stabilizing movement of the pitch drive means; and wherein the pitch drive means is disposed between the means for stabilizing movement and the pitch drive shaft.
 7. The joint of claim 6 wherein the means for stabilizing movement includes roller means engaging a surface of the pitch drive means.
 8. The joint of claim 1 wherein the first gimbal means includes:an inner gimbal member rotatably mounted to the support means and having means for transmitting motion to another inner gimbal member of the second gimbal means; an outer gimbal member rotatably mounted to the support means and having means for transmitting motion to another outer gimbal of the second gimbal means; conduit means having an internal passage and being attached to the inner gimbal member and extending through a slot of the outer gimbal member, the slot having oppositely-facing first and second surfaces, each surface having first and second tracks; first bearing means disposed about the conduit means and engaging a first track of a first surface; and second bearing means disposed about the conduit means and engaging a second track of a second surface.
 9. A mechanical joint comprising:support means having an interior; a first and a second gimbal assembly rotatably mounted within the interior, each gimbal assembly having means for transferring motion to the other gimbal assembly; drive means operatively connected to the first and second gimbal assemblies for effecting selective movement of the first and second gimbal assemblies; means for transmitting rotational movement to the joint including a drive shaft attached to the first gimbal assembly; and means for engaging the drive shaft having a member that is preloaded against and slidably engaging the drive shaft and being pivotally attached to the support means.
 10. A mechanical joint comprising:support means having an interior; a first and second gimbal assembly rotatably mounted within the interior, each gimbal assembly having means for transferring motion to the other gimbal assembly; drive means operatively connected to the first and second gimbal assemblies for effecting selective movement of the first and second gimbal assemblies; means for transmitting rotational movement to the joint; and linkage means for stabilizing the joint having a first end pivotally attached to the support means and a second end pivotally attached to a base from which the drive means extends. 